Implementing automatic switchover

ABSTRACT

One or more techniques and/or computing devices are provided for automatic switchover implementation. For example, a first storage controller, of a first storage cluster, may have a disaster recovery relationship with a second storage controller of a second storage cluster. In the event the first storage controller fails, the second storage controller may automatically switchover operation from the first storage controller to the second storage controller for providing clients with failover access to data previously accessible to the clients through the first storage controller. The second storage controller may detect, cross-cluster, a failure of the first storage controller utilizing remote direct memory access (RDMA) read operations to access heartbeat information, heartbeat information stored within a disk mailbox, and/or service processor traps. In this way, the second storage controller may efficiently detect failure of the first storage controller to trigger automatic switchover for non-disruptive client access to data.

RELATED APPLICATIONS

This application claims priority to and is a continuation of U.S.application Ser. No. 15/820,851, filed on Nov. 22, 2017, now allowed,and titled “IMPLEMENTING AUTOMATIC SWITCHOVER,” which claims priority toand is a continuation of U.S. Pat. No. 9,836,368, filed on Oct. 22, 2015and titled “IMPLEMENTING AUTOMATIC SWITCHOVER,” which are incorporatedherein by reference.

BACKGROUND

Many storage networks may implement data replication and/or otherredundancy data access techniques for data loss protection andnon-disruptive client access. For example, a first storage cluster maycomprise a first storage controller configured to provide clients withprimary access to data stored within a first storage device and/or otherstorage devices. A second storage cluster may comprise a second storagecontroller configured to provide clients with access to data storedwithin a second storage device (e.g., failover access to replicated datawithin the second storage device) and/or other storage devices (e.g.,primary access to data stored within a third storage device). The firststorage controller and the second storage controller may be configuredaccording to a disaster recovery relationship, such that the secondstorage controller may provide failover access to replicated data thatwas replicated from the first storage device to the second storagedevice (e.g., a switchover operation may be performed where the secondstorage controller assumes ownership of the second storage device and/orother storage devices previously owned by the first storage controllerso that the second storage controller may provide clients with failoveraccess to data within such storage devices).

In an example, the second storage cluster may be located at a remotesite to the first storage cluster (e.g., storage clusters may be locatedin different buildings, cities, thousands of kilometers from oneanother, etc.). Thus, if a disaster occurs at a site of a storagecluster, then a surviving storage cluster may remain unaffected by thedisaster (e.g., a power outage of a building hosting the first storagecluster may not affect a second building hosting the second storagecluster in a different city).

If the first storage cluster merely comprises the first storagecontroller and the second storage cluster merely comprises the secondstorage controller (e.g., single storage controller clusterconfigurations that may be cost effective due to clusters merelycomprising single storage controllers), then there may not be local highavailability storage controllers paired with the first storagecontroller or the second storage controller that could otherwise providerelatively fast local takeover for a failed storage controller fornon-disruptive client access to data of the failed storage controller(e.g., if the first storage cluster comprised a third storage controllerhaving a high availability pairing with the first storage controller,then the third storage controller could quickly takeover for the firststorage controller in the event the first storage controller fails).Instead, a cross cluster switchover operation may need to be performedif a storage controller fails. Cross-cluster remote detection of astorage controller failure (e.g., the second storage controller, withinthe second storage cluster, detecting a failure of the first storagecontroller within the first storage cluster) may utilize timeouts,manual switchover, and/or other relatively slow or imprecise techniquesthat may not provide adequate non-disruptive client access to data(e.g., a client may lose access to data for more than 2 minutes whilewaiting on a manual switchover from a failed storage controller to asurviving storage controller). Thus, it may be advantageous to quicklyand reliably detect storage controller failure cross-cluster forautomatic implementation of switchover operations.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a component block diagram illustrating an example clusterednetwork in accordance with one or more of the provisions set forthherein.

FIG. 2 is a component block diagram illustrating an example data storagesystem in accordance with one or more of the provisions set forthherein.

FIG. 3 is a flow chart illustrating an exemplary method of implementingautomatic switchover.

FIG. 4 is a component block diagram illustrating an exemplary computingdevice for implementing automatic switchover utilizing remote directmemory access (RDMA) read operations.

FIG. 5 is a component block diagram illustrating an exemplary computingdevice for implementing automatic switchover utilizing remote directmemory access (RDMA) read operations and disk mailboxes.

FIG. 6 is a flow chart illustrating an exemplary method of implementingautomatic switchover.

FIG. 7 is a component block diagram illustrating an exemplary computingdevice for implementing automatic switchover utilizing disk mailboxes.

FIG. 8 is a flow chart illustrating an exemplary method of implementingautomatic switchover.

FIG. 9 is a component block diagram illustrating an exemplary computingdevice for implementing automatic switchover utilizing service processortraps.

FIG. 10 is an example of a computer readable medium in accordance withone or more of the provisions set forth herein.

DETAILED DESCRIPTION

Some examples of the claimed subject matter are now described withreference to the drawings, where like reference numerals are generallyused to refer to like elements throughout. In the following description,for purposes of explanation, numerous specific details are set forth inorder to provide an understanding of the claimed subject matter. It maybe evident, however, that the claimed subject matter may be practicedwithout these specific details. Nothing in this detailed description isadmitted as prior art.

One or more techniques and/or computing devices for automatic switchoverimplementation are provided. For example, a first storage controller,within a first storage cluster, may have a disaster recoveryrelationship with a second storage controller, within a second storagecluster, such that a surviving storage controller may provide clientswith failover access to data in the event the other storage controllerfails. As provided herein, failure of a storage controller may bequickly identified cross-cluster based upon a heartbeat signal that isidentified by a surviving storage controller using a remote directmemory access (RDMA) read operation, a read operation from a diskmailbox of the failed storage controller, or receipt of a serviceprocessor trap sent by a service processor of the failed storagecontroller. Responsive to identifying failure of the failed storagecontroller, the surviving storage controller may automatically implementa switchover operation where the surviving storage controller takes overownership of storage from the failed storage controller so that thesurviving storage controller may provide clients with failover access todata within such storage.

To provide context for automatic switchover implementation, FIG. 1illustrates an embodiment of a clustered network environment 100 or anetwork storage environment. It may be appreciated, however, that thetechniques, etc. described herein may be implemented within theclustered network environment 100, a non-cluster network environment,and/or a variety of other computing environments, such as a desktopcomputing environment. That is, the instant disclosure, including thescope of the appended claims, is not meant to be limited to the examplesprovided herein. It will be appreciated that where the same or similarcomponents, elements, features, items, modules, etc. are illustrated inlater figures but were previously discussed with regard to priorfigures, that a similar (e.g., redundant) discussion of the same may beomitted when describing the subsequent figures (e.g., for purposes ofsimplicity and ease of understanding).

FIG. 1 is a block diagram illustrating an example clustered networkenvironment 100 that may implement at least some embodiments of thetechniques and/or systems described herein. The example environment 100comprises data storage systems or storage sites 102 and 104 that arecoupled over a cluster fabric 106, such as a computing network embodiedas a private Infiniband, Fibre Channel (FC), or Ethernet networkfacilitating communication between the storage systems 102 and 104 (andone or more modules, component, etc. therein, such as, nodes 116 and118, for example). It will be appreciated that while two data storagesystems 102 and 104 and two nodes 116 and 118 are illustrated in FIG. 1,that any suitable number of such components is contemplated. In anexample, nodes 116, 118 comprise storage controllers (e.g., node 116 maycomprise a primary or local storage controller and node 118 may comprisea secondary or remote storage controller) that provide client devices,such as host devices 108, 110, with access to data stored within datastorage devices 128, 130. Similarly, unless specifically providedotherwise herein, the same is true for other modules, elements,features, items, etc. referenced herein and/or illustrated in theaccompanying drawings. That is, a particular number of components,modules, elements, features, items, etc. disclosed herein is not meantto be interpreted in a limiting manner.

It will be further appreciated that clustered networks are not limitedto any particular geographic areas and can be clustered locally and/orremotely. Thus, in one embodiment a clustered network can be distributedover a plurality of storage systems and/or nodes located in a pluralityof geographic locations; while in another embodiment a clustered networkcan include data storage systems (e.g., 102, 104) residing in a samegeographic location (e.g., in a single onsite rack of data storagedevices).

In the illustrated example, one or more host devices 108, 110 which maycomprise, for example, client devices, personal computers (PCs),computing devices used for storage (e.g., storage servers), and othercomputers or peripheral devices (e.g., printers), are coupled to therespective data storage systems 102, 104 by storage network connections112, 114. Network connection may comprise a local area network (LAN) orwide area network (WAN), for example, that utilizes Network AttachedStorage (NAS) protocols, such as a Common Internet File System (CIFS)protocol or a Network File System (NFS) protocol to exchange datapackets. Illustratively, the host devices 108, 110 may begeneral-purpose computers running applications, and may interact withthe data storage systems 102, 104 using a client/server model forexchange of information. That is, the host device may request data fromthe data storage system (e.g., data on a storage device managed by anetwork storage control configured to process I/O commands issued by thehost device for the storage device), and the data storage system mayreturn results of the request to the host device via one or more networkconnections 112, 114.

The nodes 116, 118 on clustered data storage systems 102, 104 cancomprise network or host nodes that are interconnected as a cluster toprovide data storage and management services, such as to an enterprisehaving remote locations, cloud storage (e.g., a storage endpoint may bestored within a data cloud), etc., for example. Such a node in a datastorage and management network cluster environment 100 can be a deviceattached to the network as a connection point, redistribution point orcommunication endpoint, for example. A node may be capable of sending,receiving, and/or forwarding information over a network communicationschannel, and could comprise any device that meets any or all of thesecriteria. One example of a node may be a data storage and managementserver attached to a network, where the server can comprise a generalpurpose computer or a computing device particularly configured tooperate as a server in a data storage and management system.

In an example, a first storage cluster of nodes such as the nodes 116,118 (e.g., a first set of storage controllers configured to provideaccess to a first storage aggregate comprising a first logical groupingof one or more storage devices) may be located on a first storage site.A second storage cluster of nodes, not illustrated, may be located at asecond storage site (e.g., a second set of storage controllersconfigured to provide access to a second storage aggregate comprising asecond logical grouping of one or more storage devices). The firststorage cluster of nodes and the second storage cluster of nodes may beconfigured according to a disaster recovery configuration where asurviving cluster of nodes provides switchover access to storage devicesof a disaster cluster of nodes in the event a disaster occurs at adisaster storage site comprising the disaster cluster of nodes (e.g.,the first storage cluster of nodes provides client devices withswitchover data access to storage devices of the second storageaggregate in the event a disaster occurs at the second storage site).

As illustrated in the exemplary environment 100, nodes 116, 118 cancomprise various functional components that coordinate to providedistributed storage architecture for the cluster. For example, the nodescan comprise a network module 120, 122 and a data module 124, 126.Network modules 120, 122 can be configured to allow the nodes 116, 118(e.g., network storage controllers) to connect with host devices 108,110 over the network connections 112, 114, for example, allowing thehost devices 108, 110 to access data stored in the distributed storagesystem. Further, the network modules 120, 122 can provide connectionswith one or more other components through the cluster fabric 106. Forexample, in FIG. 1, a first network module 120 of first node 116 canaccess a second data storage device 130 by sending a request through asecond data module 126 of a second node 118.

Data modules 124, 126 can be configured to connect one or more datastorage devices 128, 130, such as disks or arrays of disks, flashmemory, or some other form of data storage, to the nodes 116, 118. Thenodes 116, 118 can be interconnected by the cluster fabric 106, forexample, allowing respective nodes in the cluster to access data on datastorage devices 128, 130 connected to different nodes in the cluster.Often, data modules 124, 126 communicate with the data storage devices128, 130 according to a storage area network (SAN) protocol, such asSmall Computer System Interface (SCSI) or Fiber Channel Protocol (FCP),for example. Thus, as seen from an operating system on a node 116, 118,the data storage devices 128, 130 can appear as locally attached to theoperating system. In this manner, different nodes 116, 118, etc. mayaccess data blocks through the operating system, rather than expresslyrequesting abstract files.

It should be appreciated that, while the example embodiment 100illustrates an equal number of network and data modules, otherembodiments may comprise a differing number of these modules. Forexample, there may be a plurality of network and data modulesinterconnected in a cluster that does not have a one-to-onecorrespondence between the network and data modules. That is, differentnodes can have a different number of network and data modules, and thesame node can have a different number of network modules than datamodules.

Further, a host device 108, 110 can be networked with the nodes 116, 118in the cluster, over the networking connections 112, 114. As an example,respective host devices 108, 110 that are networked to a cluster mayrequest services (e.g., exchanging of information in the form of datapackets) of a node 116, 118 in the cluster, and the node 116, 118 canreturn results of the requested services to the host devices 108, 110.In one embodiment, the host devices 108, 110 can exchange informationwith the network modules 120, 122 residing in the nodes (e.g., networkhosts) 116, 118 in the data storage systems 102, 104.

In one embodiment, the data storage devices 128, 130 comprise volumes132, which is an implementation of storage of information onto diskdrives or disk arrays or other storage (e.g., flash) as a file-systemfor data, for example. Volumes can span a portion of a disk, acollection of disks, or portions of disks, for example, and typicallydefine an overall logical arrangement of file storage on disk space inthe storage system. In one embodiment a volume can comprise stored dataas one or more files that reside in a hierarchical directory structurewithin the volume.

Volumes are typically configured in formats that may be associated withparticular storage systems, and respective volume formats typicallycomprise features that provide functionality to the volumes, such asproviding an ability for volumes to form clusters. For example, where afirst storage system may utilize a first format for their volumes, asecond storage system may utilize a second format for their volumes.

In the example environment 100, the host devices 108, 110 can utilizethe data storage systems 102, 104 to store and retrieve data from thevolumes 132. In this embodiment, for example, the host device 108 cansend data packets to the network module 120 in the node 116 within datastorage system 102. The node 116 can forward the data to the datastorage device 128 using the data module 124, where the data storagedevice 128 comprises volume 132A. In this way, in this example, the hostdevice can access the storage volume 132A, to store and/or retrievedata, using the data storage system 102 connected by the networkconnection 112. Further, in this embodiment, the host device 110 canexchange data with the network module 122 in the host 118 within thedata storage system 104 (e.g., which may be remote from the data storagesystem 102). The host 118 can forward the data to the data storagedevice 130 using the data module 126, thereby accessing volume 1328associated with the data storage device 130.

It may be appreciated that automatic switchover implementation may beimplemented within the clustered network environment 100. In an example,the node 116 (e.g., a first storage controller) may cross-cluster (e.g.,across the cluster fabric 106 or another network) detect a failure ofthe node 118 (e.g., a second storage controller) utilizing heartbeatinformation obtained through remote direct memory access (RDMA) readoperations, read operations from a disk mailbox of the node 118, and/orservice processor traps sent by a service processor of the node 118. Inthis way, the node 116 may automatically implement a switchoveroperation. It may be appreciated that automatic switchoverimplementation may be implemented for and/or between any type ofcomputing environment, and may be transferable between physical devices(e.g., node 116, node 118, etc.) and/or a cloud computing environment(e.g., remote to the clustered network environment 100).

FIG. 2 is an illustrative example of a data storage system 200 (e.g.,102, 104 in FIG. 1), providing further detail of an embodiment ofcomponents that may implement one or more of the techniques and/orsystems described herein. The example data storage system 200 comprisesa node 202 (e.g., host nodes 116, 118 in FIG. 1), and a data storagedevice 234 (e.g., data storage devices 128, 130 in FIG. 1). The node 202may be a general purpose computer, for example, or some other computingdevice particularly configured to operate as a storage server. A hostdevice 205 (e.g., 108, 110 in FIG. 1) can be connected to the node 202over a network 216, for example, to provides access to files and/orother data stored on the data storage device 234. In an example, thenode 202 comprises a storage controller that provides client devices,such as the host device 205, with access to data stored within datastorage device 234.

The data storage device 234 can comprise mass storage devices, such asdisks 224, 226, 228 of a disk array 218, 220, 222. It will beappreciated that the techniques and systems, described herein, are notlimited by the example embodiment. For example, disks 224, 226, 228 maycomprise any type of mass storage devices, including but not limited tomagnetic disk drives, flash memory, and any other similar media adaptedto store information, including, for example, data (D) and/or parity (P)information.

The node 202 comprises one or more processors 204, a memory 206, anetwork adapter 210, a cluster access adapter 212, and a storage adapter214 interconnected by a system bus 242. The storage system 200 alsoincludes an operating system 208 installed in the memory 206 of the node202 that can, for example, implement a Redundant Array of Independent(or Inexpensive) Disks (RAID) optimization technique to optimize areconstruction process of data of a failed disk in an array.

The operating system 208 can also manage communications for the datastorage system, and communications between other data storage systemsthat may be in a clustered network, such as attached to a cluster fabric215 (e.g., 106 in FIG. 1). Thus, the node 202, such as a network storagecontroller, can respond to host device requests to manage data on thedata storage device 234 (e.g., or additional clustered devices) inaccordance with these host device requests. The operating system 208 canoften establish one or more file systems on the data storage system 200,where a file system can include software code and data structures thatimplement a persistent hierarchical namespace of files and directories,for example. As an example, when a new data storage device (not shown)is added to a clustered network system, the operating system 208 isinformed where, in an existing directory tree, new files associated withthe new data storage device are to be stored. This is often referred toas “mounting” a file system.

In the example data storage system 200, memory 206 can include storagelocations that are addressable by the processors 204 and adapters 210,212, 214 for storing related software application code and datastructures. The processors 204 and adapters 210, 212, 214 may, forexample, include processing elements and/or logic circuitry configuredto execute the software code and manipulate the data structures. Theoperating system 208, portions of which are typically resident in thememory 206 and executed by the processing elements, functionallyorganizes the storage system by, among other things, invoking storageoperations in support of a file service implemented by the storagesystem. It will be apparent to those skilled in the art that otherprocessing and memory mechanisms, including various computer readablemedia, may be used for storing and/or executing application instructionspertaining to the techniques described herein. For example, theoperating system can also utilize one or more control files (not shown)to aid in the provisioning of virtual machines.

The network adapter 210 includes the mechanical, electrical andsignaling circuitry needed to connect the data storage system 200 to ahost device 205 over a computer network 216, which may comprise, amongother things, a point-to-point connection or a shared medium, such as alocal area network. The host device 205 (e.g., 108, 110 of FIG. 1) maybe a general-purpose computer configured to execute applications. Asdescribed above, the host device 205 may interact with the data storagesystem 200 in accordance with a client/host model of informationdelivery.

The storage adapter 214 cooperates with the operating system 208executing on the node 202 to access information requested by the hostdevice 205 (e.g., access data on a storage device managed by a networkstorage controller). The information may be stored on any type ofattached array of writeable media such as magnetic disk drives, flashmemory, and/or any other similar media adapted to store information. Inthe example data storage system 200, the information can be stored indata blocks on the disks 224, 226, 228. The storage adapter 214 caninclude input/output (I/O) interface circuitry that couples to the disksover an I/O interconnect arrangement, such as a storage area network(SAN) protocol (e.g., Small Computer System Interface (SCSI), iSCSI,hyperSCSI, Fiber Channel Protocol (FCP)). The information is retrievedby the storage adapter 214 and, if necessary, processed by the one ormore processors 204 (or the storage adapter 214 itself) prior to beingforwarded over the system bus 242 to the network adapter 210 (and/or thecluster access adapter 212 if sending to another node in the cluster)where the information is formatted into a data packet and returned tothe host device 205 over the network connection 216 (and/or returned toanother node attached to the cluster over the cluster fabric 215).

In one embodiment, storage of information on arrays 218, 220, 222 can beimplemented as one or more storage “volumes” 230, 232 that are comprisedof a cluster of disks 224, 226, 228 defining an overall logicalarrangement of disk space. The disks 224, 226, 228 that comprise one ormore volumes are typically organized as one or more groups of RAIDs. Asan example, volume 230 comprises an aggregate of disk arrays 218 and220, which comprise the cluster of disks 224 and 226.

In one embodiment, to facilitate access to disks 224, 226, 228, theoperating system 208 may implement a file system (e.g., write anywherefile system) that logically organizes the information as a hierarchicalstructure of directories and files on the disks. In this embodiment,respective files may be implemented as a set of disk blocks configuredto store information, whereas directories may be implemented asspecially formatted files in which information about other files anddirectories are stored.

Whatever the underlying physical configuration within this data storagesystem 200, data can be stored as files within physical and/or virtualvolumes, which can be associated with respective volume identifiers,such as file system identifiers (FSIDs), which can be 32-bits in lengthin one example.

A physical volume corresponds to at least a portion of physical storagedevices whose address, addressable space, location, etc. doesn't change,such as at least some of one or more data storage devices 234 (e.g., aRedundant Array of Independent (or Inexpensive) Disks (RAID system)).Typically the location of the physical volume doesn't change in that the(range of) address(es) used to access it generally remains constant.

A virtual volume, in contrast, is stored over an aggregate of disparateportions of different physical storage devices. The virtual volume maybe a collection of different available portions of different physicalstorage device locations, such as some available space from each of thedisks 224, 226, and/or 228. It will be appreciated that since a virtualvolume is not “tied” to any one particular storage device, a virtualvolume can be said to include a layer of abstraction or virtualization,which allows it to be resized and/or flexible in some regards.

Further, a virtual volume can include one or more logical unit numbers(LUNs) 238, directories 236, Qtrees 235, and files 240. Among otherthings, these features, but more particularly LUNS, allow the disparatememory locations within which data is stored to be identified, forexample, and grouped as data storage unit. As such, the LUNs 238 may becharacterized as constituting a virtual disk or drive upon which datawithin the virtual volume is stored within the aggregate. For example,LUNs are often referred to as virtual drives, such that they emulate ahard drive from a general purpose computer, while they actually comprisedata blocks stored in various parts of a volume.

In one embodiment, one or more data storage devices 234 can have one ormore physical ports, wherein each physical port can be assigned a targetaddress (e.g., SCSI target address). To represent respective volumesstored on a data storage device, a target address on the data storagedevice can be used to identify one or more LUNs 238. Thus, for example,when the node 202 connects to a volume 230, 232 through the storageadapter 214, a connection between the node 202 and the one or more LUNs238 underlying the volume is created.

In one embodiment, respective target addresses can identify multipleLUNs, such that a target address can represent multiple volumes. The I/Ointerface, which can be implemented as circuitry and/or software in thestorage adapter 214 or as executable code residing in memory 206 andexecuted by the processors 204, for example, can connect to volume 230by using one or more addresses that identify the LUNs 238.

It may be appreciated that automatic switchover implementation may beimplemented for the data storage system 200. In an example, the node 202(e.g., a first storage controller) may cross-cluster (e.g., across thecluster fabric 215 or another network) detect a failure of a second node(e.g., a second storage controller) utilizing heartbeat informationobtained through remote direct memory access (RDMA) read operations,read operations from a disk mailbox of the second node, and/or serviceprocessor traps sent by a service processor of the second node. It maybe appreciated that automatic switchover implementation may beimplemented for and/or between any type of computing environment, andmay be transferable between physical devices (e.g., node 202, host 205,etc.) and/or a cloud computing environment (e.g., remote to the node 202and/or the host 205).

One embodiment of automatic switchover implementation is illustrated byan exemplary method 300 of FIG. 3. A first storage cluster may comprisea first storage controller configured to provide clients with primaryaccess to data stored within a first storage device and/or other storagedevices. In an example, the first storage cluster has a singlecontroller cluster configuration such that the first storage clustermerely comprises the first storage controller (e.g., but may lack alocal high availability controller paired to the first storagecontroller for local failover). A second storage cluster may comprise asecond storage controller configured as a disaster recovery partner forthe first storage controller. For example, upon detecting a failure ofthe first storage controller (e.g., a disaster at the first storagecluster), the second storage controller may perform a switchoveroperation to obtain ownership of storage devices, owned by the firststorage controller, so that the second storage controller may provideclients with failover access to such storage devices now owned by thesecond storage controller based upon the switchover operation. Uponrecovery of the first storage controller, a switchback operation may beperformed to return ownership of the storage devices back to the firststorage controller so that the first storage controller can provideclients with primary access to such storage devices. In an example, thesecond storage cluster has the single controller cluster configurationsuch that the second storage cluster merely comprises the second storagecontroller (e.g., a lack of a local high availability controllerpartner).

As provided herein, a surviving storage controller may efficientlydetect, cross-cluster, failure of a remote storage controller (e.g., thesecond storage controller detecting failure of the first storagecontroller) so that automatic switchover may be performed in a mannerthat satisfies client non-disruptive operation metrics (e.g., less thana 2 minute disruption of client access to data within the storagedevices).

At 302, the method 300 starts. At 304, a memory section (e.g., a portionof memory associated with the first storage controller) may bedesignated for heartbeat information exchange from the first storagecontroller to the second storage controller. The heartbeat informationexchange may be used by the first storage controller to conveyoperational health information of the first storage controller to thesecond storage controller. For example, the first storage controller maystore a series of sequence numbers over time to indicate progress of thefirst storage controller (e.g., if the series of sequences numbers hasnot been updated within a threshold time, then the second storagecontroller may determine that the first storage controller may have hada failure, such as a software panic, a storage controller halt, astorage controller reboot, and/or other state transitions of the firststorage controller from a normal operating state to a failure state). Inthis way, heartbeat status information may be conveyed to the secondstorage controller through the memory section.

At 306, the second storage controller may perform a remote direct memoryaccess (RDMA) read operation to access the memory section for obtaininga current heartbeat status of the first storage controller. The currentheartbeat status may comprise a new sequence number indicating progressof the first storage controller, a prior sequence number indicative of alack of progress by the first storage controller, a normal operatingstate indication, a state transition indication, a software panicindication, a storage controller halt indication, a storage controllerreboot indication, etc.

At 308, responsive to the current heartbeat status indicating a failureof the first storage controller, an automatic switchover operation maybe performed. For example, the second storage controller mayautomatically trigger the switchover operation to obtain ownership ofstorage devices owned by the first storage controller. In this way, thesecond storage controller may provide clients with failover access tothe storage devices so that clients are provided with non-disruptiveaccess to data.

In an example, one or more checks may be performed before triggering theautomatic switchover operation. For example, a communication signal maybe sent from the second storage controller to the first storage cluster.Responsiveness to the communication signal may be evaluated to determinewhether the failure is a false trigger (e.g., the first storage clustermay respond with an indication that the first storage controller is inan operational state). If the failure is a false trigger, then theautomatic switchover may not be performed. If the failure is not a falsetrigger, then the automatic switchover operation may be performed and/orother checks may be performed. For example, responsive to determiningthat the failure is not the false trigger, a determination may be madeas to whether storage and/or a main controller (e.g., a main box) of thefirst storage cluster are available. Responsive to the storage and/orthe main controller not being available, a manual switchover operationmay be performed instead of the automatic switchover operation.Responsive to the storage and/or the main controller being available,the automatic switchover operation may be performed and/or other checksmay be performed. For example, a write caching synchronization statebetween the first storage controller and the second storage controllermay be evaluated (e.g., the first storage controller may temporarilystore information relating to client I/O operations, such as writerequest, within a write request cache before flushing to disk, which maybe mirrored to the second storage controller so that up-to-date cachedclient I/O operations, not yet flushed to disk, are accounted for by thesecond storage controller in the event of a switchover). The writecaching synchronization state may be read from a first disk mailbox ofthe first storage controller (e.g., a raw read may be performed upon astorage device, owned by the first storage controller but not the secondstorage controller, hosting the first disk mailbox). Responsive to thewrite caching synchronization state indicating a synchronous state, theautomatic switchover may be performed. Responsive to the write cachingsynchronization state indicating a non-synchronous state, the automaticswitchover may not be performed.

In an example, heartbeat status information may also be obtained fromthe first disk mailbox corresponding to the storage device owned by thefirst storage controller, but not the second storage controller. Eventhough the second storage controller does not own the storage devicehosting the first disk mailbox, the second storage controller mayperform raw read operations to the first disk mailbox to obtainheartbeat status information. For example, second current heartbeatstatus information may be read from the first disk mailbox. Responsiveto the current heartbeat status and/or the second current heartbeatstatus indicating the failure, the automatic switchover operation may beimplemented (e.g., the second current heartbeat status may indicate apower loss failure of the first storage controller). For example, theautomatic switchover operation may be initiated after a thresholdtimeout from the second current heartbeat status being indicative of thefailure. At 310, the method 300 ends.

FIG. 4 illustrates an example of a system 400 for automatic switchoverimplementation. A first storage cluster 406 may comprise a first storagecontroller 402 and a second storage cluster 414 may comprise a secondstorage controller 410. The first storage controller 402 and the secondstorage controller 410 may be configured as disaster recovery partners.The first storage cluster 406 and the second storage cluster 414 may beconnected by a network 408. The first storage controller 402 may storeheartbeat status information, such as a series of sequence numbersindicative of progress of the first storage controller 402, statetransition information, operating state information, etc., within afirst memory section 404. The second storage controller 410 may performremote direct memory access (RDMA) read operations to the first memorysection 404 to obtain current heartbeat status information of the firststorage controller 402. Responsive to the current heartbeat statusinformation indicating a failure of the first storage controller 402,the second storage controller 410 may automatically implement aswitchover operation to takeover processing client I/O requestspreviously processed by the first storage controller 402 before thefailure.

The second storage controller 410 may store heartbeat statusinformation, such as a series of sequence numbers indicative of progressof the second storage controller 410, state transition information,operating state information, etc., within a second memory section 412.The first storage controller 402 may perform remote direct memory access(RDMA) read operations to the second memory section 412 to obtaincurrent heartbeat status information of the second storage controller410. Responsive to the current heartbeat status information indicating afailure of the second storage controller 410, the first storagecontroller 402 may automatically implement a switchover operation totakeover processing client I/O requests previously processed by thesecond storage controller 410 before the failure.

FIG. 5 illustrates an example of a system 500 for automatic switchoverimplementation. A first storage cluster 506 may comprise a first storagecontroller 502 and a second storage cluster 514 may comprise a secondstorage controller 510. The first storage controller 502 and the secondstorage controller 510 may be configured as disaster recovery partners.The first storage cluster 506 and the second storage cluster 514 may beconnected by a network 508.

In an example of conveying heartbeat status information to the secondstorage controller 510, the first storage controller 502 may storeheartbeat status information, such as a series of sequence numbersindicative of progress of the first storage controller 502, statetransition information, operating state information, etc., within afirst memory section 504. The second storage controller 510 may performremote direct memory access (RDMA) read operations to the first memorysection 504 to obtain current heartbeat status information of the firststorage controller 502. In another example of conveying heartbeat statusinformation to the second storage controller 510, the first storagecontroller 502 may store second heartbeat status information within afirst disk mailbox 516 (e.g., a storage device owned by the firststorage controller 502 and accessible through raw read operations by thesecond storage controller that is a non-owner of the storage device).The second storage controller 510 may perform a raw read operation tothe first disk mailbox 516 to obtain second current heartbeat statusinformation of the first storage controller 502. In this way, both thefirst memory section 504 and the first disk mailbox 516 are used toconvey health information of the first storage controller 502.Responsive to the current heartbeat status information and/or the secondcurrent heartbeat status information indicating a failure of the firststorage controller 502, the second storage controller 510 mayautomatically implement a switchover operation to takeover processingclient I/O requests previously processed by the first storage controller502 before the failure.

In an example of conveying heartbeat status information to the firststorage controller 502, the second storage controller 510 may storeheartbeat status information, such as a series of sequence numbersindicative of progress of the second storage controller 510, statetransition information, operating state information, etc., within asecond memory section 512. The first storage controller 502 may performremote direct memory access (RDMA) read operations to the second memorysection 512 to obtain current heartbeat status information of the secondstorage controller 510. In another example of conveying heartbeat statusinformation to the first storage controller 502, the second storagecontroller 510 may store second heartbeat status information within asecond disk mailbox 520. The first storage controller 502 may perform araw read operation to the second disk mailbox 520 to obtain secondcurrent heartbeat status information of the second storage controller510. In this way, both the second memory section 512 and the second diskmailbox 520 are used to convey health information of the second storagecontroller 510. Responsive to the current heartbeat status informationand/or the second current heartbeat status information indicating afailure of the second storage controller 510, the first storagecontroller 502 may automatically implement a switchover operation totakeover processing client I/O requests previously processed by thesecond storage controller 510 before the failure.

One embodiment of automatic switchover implementation is illustrated byan exemplary method 600 of FIG. 6. A first storage cluster may comprisea first storage controller configured to provide clients with primaryaccess to data stored within one or more storage devices. In an example,the first storage cluster has a single controller cluster configurationsuch that the first storage cluster merely comprises the first storagecontroller and no local high availability partner controller. A secondstorage cluster may comprise a second storage controller configured as adisaster recovery partner for the first storage controller. For example,upon detecting a failure of the first storage controller, the secondstorage controller may perform a switchover operation to obtainownership of storage devices, owned by the first storage controller, sothat the second storage controller may provide clients with failoveraccess to such storage devices now owned by the second storagecontroller based upon the switchover operation. In an example, thesecond storage cluster has the single controller cluster configurationsuch that the second storage cluster merely comprises the second storagecontroller and no local high availability partner controller. Asprovided herein, a surviving storage controller may efficiently detect,cross-cluster, failure of a remote storage controller so that automaticswitchover may be performed in a manner that satisfies clientnon-disruptive operation metrics.

At 602, the method 600 starts. At 604, a first disk mailbox may bespecified for the use of heartbeat information exchange from the firststorage controller to the second storage controller. For example, thefirst storage controller may store a series of sequences numbersindicative of progress by the first storage controller, a statetransition (e.g., a transition into a software panic, a storagecontroller halt, a storage controller reboot, etc.), an indication of anormal operating state, etc. within the first disk mailbox. The firstdisk mailbox may be owned by the first storage controller and not thesecond storage controller. Even though the second storage controllerdoes not own the first disk mailbox, the second storage controller mayperform a read operation (e.g., a raw read operation) to obtain acurrent heartbeat status from the first disk mailbox, at 606.

At 608, responsive to the current heartbeat status indicating a failureof the first storage controller, an automatic switchover operation maybe performed. For example, the second storage controller mayautomatically trigger the switchover operation to obtain ownership ofstorage devices owned by the first storage controller. In this way, thesecond storage controller may provide clients with failover access tothe storage devices so that clients are provided with non-disruptiveaccess to data.

In an example, one or more checks may be performed before triggering theautomatic switchover operation. For example, a communication signal maybe sent from the second storage controller to the first storage cluster.Responsiveness to the communication signal may be evaluated to determinewhether the failure is a false trigger (e.g., the first storage clustermay respond with an indication that the first storage controller is inan operational state). If the failure is a false trigger, then theautomatic switchover may not be performed. If the failure is not a falsetrigger, then the automatic switchover operation may be performed and/orother checks may be performed. For example, responsive to determiningthat the failure is not the false trigger, a determination may be madeas to whether storage and/or a main controller (e.g., a main box) of thefirst storage cluster are available. Responsive to the storage and/orthe main controller not being available, a manual switchover operationmay be performed instead of the automatic switchover operation.Responsive to the storage and/or the main controller being available,the automatic switchover operation may be performed and/or other checksmay be performed. For example, a write caching synchronization statebetween the first storage controller and the second storage controllermay be evaluated. The write caching synchronization state may be readfrom the first disk mailbox of the first storage controller (e.g., a rawread may be performed upon a storage device, owned by the first storagecontroller but not the second storage controller, hosting the first diskmailbox). Responsive to the write caching synchronization stateindicating a synchronous state between a first write cache of the firststorage controller and a second write cache of the second storagecontroller, the automatic switchover may be performed. Responsive to thewrite caching synchronization state indicating a non-synchronous state,the automatic switchover may not be performed.

In an example, heartbeat status information may also be obtained from amemory section of the first storage controller. For example, the secondstorage controller may perform a remote direct memory access (RDMA) readoperation to the memory section to obtain a second current heartbeatstatus of the first storage controller. Responsive to the currentheartbeat status and/or the second current heartbeat status indicatingthe failure, the automatic switchover operation may be implemented. At610, the method 600 ends.

FIG. 7 illustrates an example of a system 700 for automatic switchoveroperation implementation. A first storage cluster 706 may comprise afirst storage controller 702 and a second storage cluster 714 maycomprise a second storage controller 710. The first storage controller702 and the second storage controller 710 may be configured as disasterrecovery partners. The first storage cluster 706 and the second storagecluster 714 may be connected by a network 708.

The first storage controller 702 may store heartbeat status information,such as a series of sequence numbers indicative of progress of the firststorage controller 702, state transition information, operating stateinformation, etc., within a first disk mailbox 704 (e.g., a storagedevice owned by the first storage controller 702 and accessible throughraw read operations by the second storage controller that is a non-ownerof the storage device). The second storage controller 710 may perform araw read operation to the first disk mailbox to obtain current heartbeatstatus information of the first storage controller 702. Responsive tothe current heartbeat status information indicating a failure of thefirst storage controller 702, the second storage controller 710 mayautomatically implement a switchover operation to takeover processingclient I/O requests previously processed by the first storage controller702 before the failure.

The second storage controller 710 may store heartbeat statusinformation, such as a series of sequence numbers indicative of progressof the second storage controller 710, state transition information,operating state information, etc., within a second disk mailbox 712. Thefirst storage controller 702 may perform a raw read operation to thesecond disk mailbox 712 to obtain current heartbeat status informationof the second storage controller 710. Responsive to the currentheartbeat status information indicating a failure of the second storagecontroller 710, the first storage controller 702 may automaticallyimplement a switchover operation to takeover processing client I/Orequests previously processed by the second storage controller 710before the failure.

One embodiment of automatic switchover implementation is illustrated byan exemplary method 800 of FIG. 8. A first storage cluster may comprisea first storage controller configured to provide clients with primaryaccess to data stored within one or more storage devices. In an example,the first storage cluster has a single controller cluster configurationsuch that the first storage cluster merely comprises the first storagecontroller and no local high availability controller partner. The firststorage controller may comprise a first storage processor (e.g., amicrocontroller comprising an operating system, functionality used tomonitor health of the first storage controller, and/or a battery forpower in the event the first storage controller loses power). A secondstorage cluster may comprise a second storage controller configured as adisaster recovery partner for the first storage controller. For example,upon detecting a failure of the first storage controller, the secondstorage controller may perform a switchover operation to obtainownership of storage devices, owned by the first storage controller, sothat the second storage controller may provide clients with failoveraccess to such storage devices now owned by the second storagecontroller based upon the switchover operation. In an example, thesecond storage cluster has the single controller cluster configurationsuch that the second storage cluster merely comprises the second storagecontroller and no local high availability controller partner. The secondstorage controller may comprise a second storage processor (e.g., amicrocontroller comprising an operating system, functionality used tomonitor health of the second storage controller, and/or a battery forpower in the event the second storage controller loses power). Asprovided herein, a surviving storage controller may efficiently detect,cross-cluster, failure of a remote storage controller so that automaticswitchover may be performed in a manner that satisfies clientnon-disruptive operation metrics.

At 802, the method 800 starts. At 804, an internet protocol (IP) addressand/or other communication information (e.g., a port number,authentication information such as a shared secret, etc.) of the secondstorage controller (e.g., and/or the second service processor) may bestored by the first storage controller, such as into a locationaccessible to the first service processor. At 806, the first storageprocessor may monitor health of the first storage controller. At 808,responsive to detecting a failure of the first storage controller (e.g.,a power loss, which may not affect the first storage processor becausethe first storage processor may have a battery for reserve power), aservice processor trap may be sent by the first service processor to theIP address and/or the port number. In an example, the service processortrap may include the authentication information for authentication bythe second storage controller. The service processor trap may triggerthe second storage controller to initiate an automatic switchoveroperation from the first storage controller to the second storagecontroller for providing clients with failover access to data previouslyaccessible to the clients through the first storage controller beforethe switchover. At 810, the method 800 ends.

FIG. 9 illustrates an example of a system 900 for automatic switchoverimplementation. A first storage cluster 906 may comprise a first storagecontroller 902 and a second storage cluster 914 may comprise a secondstorage controller 910. The first storage controller 902 and the secondstorage controller 910 may be configured as disaster recovery partners.The first storage cluster 906 and the second storage cluster 914 may beconnected by a network 908.

The first storage controller 902 may comprise a first service processor904 configured to monitor health of the first storage controller 902 sothat the first service processor 904 may alert the second storagecontroller 910 and/or the second service processor 912 of a failure ofthe first storage controller 902. For example, the first serviceprocessor 904 may store an IP address, a port number, and/orauthentication information used to communicate with the second storagecontroller 910 and/or the second service processor 912. Responsive tothe first service processor 904 detecting a failure of the first storagecontroller 902, such as a power loss, the first service processor 904may send a service processor trap to the second storage controller 910and/or the second service processor 912 using the IP address, the portnumber, and/or the authentication information. The service processortrap may trigger the second storage controller 910 to initiate anautomatic switchover operation from the first storage controller 902 tothe second storage controller 910 for providing clients with failoveraccess to data previously accessible to the clients through the firststorage controller 902 before switchover.

The second storage controller 910 may comprise a second serviceprocessor 912 configured to monitor health of the second storagecontroller 910 so that the second service processor 912 may alert thefirst storage controller 902 and/or the first service processor 904 of afailure of the second storage controller 910. For example, the secondservice processor 912 may store an IP address, a port number, and/orauthentication information used to communicate with the first storagecontroller 902 and/or the first service processor 904. Responsive to thesecond service processor 912 detecting a failure of the second storagecontroller 910, such as a power loss, the second service processor 912may send a service processor trap to the first storage controller 902and/or the first service processor 904 using the IP address, the portnumber, and/or the authentication information. The service processortrap may trigger the first storage controller 902 to initiate anautomatic switchover operation from the second storage controller 910 tothe first storage controller 902 for providing clients with failoveraccess to data previously accessible to the clients through the secondstorage controller 910 before switchover.

Still another embodiment involves a computer-readable medium comprisingprocessor-executable instructions configured to implement one or more ofthe techniques presented herein. An example embodiment of acomputer-readable medium or a computer-readable device that is devisedin these ways is illustrated in FIG. 10, wherein the implementation 1000comprises a computer-readable medium 1008, such as a CD-R, DVD-R, flashdrive, a platter of a hard disk drive, etc., on which is encodedcomputer-readable data 1006. This computer-readable data 1006, such asbinary data comprising at least one of a zero or a one, in turncomprises a set of computer instructions 1004 configured to operateaccording to one or more of the principles set forth herein. In someembodiments, the processor-executable computer instructions 1004 areconfigured to perform a method 1002, such as at least some of theexemplary method 300 of FIG. 3, at least some of the exemplary method600 of FIG. 6, and/or at least some of the exemplary method 800 of FIG.8, for example. In some embodiments, the processor-executableinstructions 1004 are configured to implement a system, such as at leastsome of the exemplary system 400 of FIG. 4, at least some of theexemplary system 500 of FIG. 5, at least some of the exemplary system700 of FIG. 7, and/or at least some of the exemplary system 900 of FIG.9, for example. Many such computer-readable media are contemplated tooperate in accordance with the techniques presented herein.

It will be appreciated that processes, architectures and/or proceduresdescribed herein can be implemented in hardware, firmware and/orsoftware. It will also be appreciated that the provisions set forthherein may apply to any type of special-purpose computer (e.g., filehost, storage server and/or storage serving appliance) and/orgeneral-purpose computer, including a standalone computer or portionthereof, embodied as or including a storage system. Moreover, theteachings herein can be configured to a variety of storage systemarchitectures including, but not limited to, a network-attached storageenvironment and/or a storage area network and disk assembly directlyattached to a client or host computer. Storage system should thereforebe taken broadly to include such arrangements in addition to anysubsystems configured to perform a storage function and associated withother equipment or systems.

In some embodiments, methods described and/or illustrated in thisdisclosure may be realized in whole or in part on computer-readablemedia. Computer readable media can include processor-executableinstructions configured to implement one or more of the methodspresented herein, and may include any mechanism for storing this datathat can be thereafter read by a computer system. Examples of computerreadable media include (hard) drives (e.g., accessible via networkattached storage (NAS)), Storage Area Networks (SAN), volatile andnon-volatile memory, such as read-only memory (ROM), random-accessmemory (RAM), EEPROM and/or flash memory, CD-ROMs, CD-Rs, CD-RWs, DVDs,cassettes, magnetic tape, magnetic disk storage, optical or non-opticaldata storage devices and/or any other medium which can be used to storedata.

Although the subject matter has been described in language specific tostructural features or methodological acts, it is to be understood thatthe subject matter defined in the appended claims is not necessarilylimited to the specific features or acts described above. Rather, thespecific features and acts described above are disclosed as exampleforms of implementing at least some of the claims.

Various operations of embodiments are provided herein. The order inwhich some or all of the operations are described should not beconstrued to imply that these operations are necessarily orderdependent. Alternative ordering will be appreciated given the benefit ofthis description. Further, it will be understood that not all operationsare necessarily present in each embodiment provided herein. Also, itwill be understood that not all operations are necessary in someembodiments.

Furthermore, the claimed subject matter is implemented as a method,apparatus, or article of manufacture using standard application orengineering techniques to produce software, firmware, hardware, or anycombination thereof to control a computer to implement the disclosedsubject matter. The term “article of manufacture” as used herein isintended to encompass a computer application accessible from anycomputer-readable device, carrier, or media. Of course, manymodifications may be made to this configuration without departing fromthe scope or spirit of the claimed subject matter.

As used in this application, the terms “component”, “module,” “system”,“interface”, and the like are generally intended to refer to acomputer-related entity, either hardware, a combination of hardware andsoftware, software, or software in execution. For example, a componentincludes a process running on a processor, a processor, an object, anexecutable, a thread of execution, an application, or a computer. By wayof illustration, both an application running on a controller and thecontroller can be a component. One or more components residing within aprocess or thread of execution and a component may be localized on onecomputer or distributed between two or more computers.

Moreover, “exemplary” is used herein to mean serving as an example,instance, illustration, etc., and not necessarily as advantageous. Asused in this application, “or” is intended to mean an inclusive “or”rather than an exclusive “or”. In addition, “a” and “an” as used in thisapplication are generally be construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. Also, at least one of A and B and/or the like generally means A orB and/or both A and B. Furthermore, to the extent that “includes”,“having”, “has”, “with”, or variants thereof are used, such terms areintended to be inclusive in a manner similar to the term “comprising”.

Many modifications may be made to the instant disclosure withoutdeparting from the scope or spirit of the claimed subject matter. Unlessspecified otherwise, “first,” “second,” or the like are not intended toimply a temporal aspect, a spatial aspect, an ordering, etc. Rather,such terms are merely used as identifiers, names, etc. for features,elements, items, etc. For example, a first set of information and asecond set of information generally correspond to set of information Aand set of information B or two different or two identical sets ofinformation or the same set of information.

Also, although the disclosure has been shown and described with respectto one or more implementations, equivalent alterations and modificationswill occur to others skilled in the art based upon a reading andunderstanding of this specification and the annexed drawings. Thedisclosure includes all such modifications and alterations and islimited only by the scope of the following claims. In particular regardto the various functions performed by the above described components(e.g., elements, resources, etc.), the terms used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (e.g., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure. In addition, while aparticular feature of the disclosure may have been disclosed withrespect to only one of several implementations, such feature may becombined with one or more other features of the other implementations asmay be desired and advantageous for any given or particular application.

What is claimed is:
 1. A method comprising: determining that a diskmailbox and a memory storage section are designated for heartbeatinformation exchange from a first node to a second node; reading a firstcurrent heartbeat status of the first node from the disk mailbox;performing a remote direct memory access read operation to read a secondcurrent heartbeat status of the first node from the memory storagesection; determining a write caching synchronization state between thefirst node and the second node based upon a combination of the first andsecond current heartbeat statuses indicating a failure of the firstnode; and refraining from initiating an automatic switchover operationbased upon the write caching synchronization state indicating anon-synchronous state.
 2. The method of claim 1, comprising: refrainingfrom initiating the automatic switch over operation if the first currentheartbeat status indicates that the first node is operational and thesecond current heartbeat status indicates that the first node hasfailed.
 3. The method of claim 1, comprising: reading the write cachingsynchronization state from the disk mailbox of the first node.
 4. Themethod of claim 1, comprising: refraining from initiating the automaticswitch over operation if the second current heartbeat status indicatesthat the first node is operational and the first current heartbeatstatus indicates that the first node has failed.
 5. The method of claim1, wherein the first current heartbeat status specifies a storagecontroller reboot as the failure.
 6. The method of claim 1, wherein thefirst current heartbeat status specifies a state transition of the firstnode.
 7. The method of claim 1, wherein the heartbeat informationexchange corresponds to a series of sequence numbers used to indicateprogress of the first node.
 8. The method of claim 1, comprising:evaluating responsiveness to a communication signal sent from the secondnode to the first node to determine whether the failure is a falsetrigger.
 9. The method of claim 1, comprising: initiating a manualswitchover operation based upon a determination that storage and a maincontroller of a cluster comprising the first node are unavailable. 10.The method of claim 1, wherein the first node is configured according toa single controller cluster configuration and the second node isconfigured according to the single controller cluster configuration. 11.The method of claim 10, comprising: determining the failure as a powerloss failure based upon both the first current heartbeat status and thesecond current heartbeat status indicating the failure.
 12. The methodof claim 11, comprising: initiating the automatic switchover operationafter a threshold timeout based upon both the first current heartbeatstatus and the second current heartbeat status indicating the failure.13. A non-transitory machine readable medium comprising machineexecutable code which when executed by a machine, causes the machine to:determine that a storage section is designated for heartbeat informationexchange from a first node to a second node; perform a read operation toaccess the storage section for obtaining a current heartbeat status ofthe first node; determine a write caching synchronization state betweenthe first node and the second node based upon the current heartbeatstatus indicating a failure of the first node; refrain from initiatingan automatic switchover operation based upon the write cachingsynchronization state indicating that the second node has not accountedfor client I/O operations temporarily stored by the first node within awrite cache before being written to a storage device by the first node;and in response to the write caching synchronization state indicatingthat the second node has accounted for the client I/O operations and isin a synchronous state, initiating the automatic switchover.
 14. Thenon-transitory machine readable medium of claim 13, wherein the storagesection comprises a memory section accessible by a remote direct memoryaccess read operation.
 15. The non-transitory machine readable medium ofclaim 13, wherein the machine executable code causes the machine to:reading the write caching synchronization state from a disk mailbox ofthe first node.
 16. The non-transitory machine readable medium of claim13, wherein the storage section comprises a disk mailbox and the currentheartbeat status is read from the disk mailbox.
 17. The non-transitorymachine readable medium of claim 13, wherein the current heartbeatstatus specifies a storage controller reboot as the failure.
 18. Thenon-transitory machine readable medium of claim 13, wherein the currentheartbeat status specifies a state transition of the first node.
 19. Acomputing device comprising: a memory comprising machine executablecode; and a service processor coupled to the memory, the serviceprocessor configured to execute the machine executable code to cause theservice processor to: store an internet protocol (IP) address of asecond storage controller that is within a second storage cluster, thesecond storage controller configured as a disaster recovery partner fora first storage controller that is within a first storage cluster;monitor health of the first storage controller; detect a failure of thefirst storage controller; generate a service processor trap based uponthe IP address, a port number of the second controller, and a sharedsecret within authentication information for the second storagecontroller; and send the service processor trap to the IP address, theservice processor trap triggering the second storage controller toinitiate an automatic switchover operation from the first storagecontroller to the second storage controller for providing clients withfailover access to data previously accessible to the clients through thefirst storage controller before switchover.
 20. The computing device ofclaim 19, wherein the service processor comprises a battery used topower the service processor in the event the first storage controllerloses power.